1. The small intestine performs a diverse set of functions.
2. Small bowel obstruction is one of the most common surgical diagnoses.
3. Most cases of small bowel obstruction are due to adhesions from
4. If, following surgical resection, less than 200 cm of small bowel
remains, patients are at risk of developing short bowel syndrome.
5. Tumors and malignancies of the small bowel are rare and difficult
The small intestine is the raison d’être of
the GI tract as it is the principle site of nutrient digestion and
absorption.1 The small intestine is also the body’s
largest reservoir of immunologically active and hormone-producing
cells, and hence can be conceptualized as the largest organ of the
immune and endocrine systems, respectively. It achieves this diversity
of action through unique anatomical features that provide it with
a massive surface area, a diversity of cell types, and a complex
neural network to coordinate these functions.
Despite its size and importance, diseases of the small intestine
are relatively infrequent, and present diagnostic and therapeutic
challenges. Treatments for common conditions such as postoperative ileus
are hardly more effective than those used at the dawn of the last
century. Mortality rates associated with acute mesenteric ischemia
have not improved during the past 50 years.
Despite the introduction of novel imaging techniques such as capsule
endoscopy and double balloon endoscopy, diagnostic tests lack sufficient
predictive power to definitively guide clinical decision making
for individual patients. Furthermore, few high-quality, controlled
data on the efficacy of surgical therapies for small bowel diseases
Therefore, sound clinical judgment and a thorough understanding of
anatomy, physiology, and pathophysiology remain essential to the
care of patients with intestinal disorders.
The small intestine is a tubular structure that extends from
the pylorus to the cecum. The estimated length of this structure
varies depending on whether radiologic, surgical, or autopsy measurements are
made. In the living, it is thought to measure 4 to 6 m.2 The
small intestine consists of three segments lying in series: the
duodenum, jejunum, and ileum. The duodenum, the most proximal segment,
lies in the retroperitoneum immediately adjacent to the head and
inferior border of the body of the pancreas. The duodenum is demarcated from
the stomach by the pylorus and from the jejunum by the ligament
of Treitz. The jejunum and ileum lie within the peritoneal cavity
and are tethered to the retroperitoneum by a broad-based mesentery.
No distinct anatomic landmark demarcates the jejunum from the ileum;
the proximal 40% of the jejunoileal segment is arbitrarily
defined as the jejunum and the distal 60% as the ileum.
The ileum is demarcated from the cecum by the ileocecal valve.
The small intestine contains mucosal folds known as plicae
circulares or valvulae conniventes that
are visible upon gross inspection. These ...